Exciting look at the kinetics/chemical mechanism of ethylene oxidation.
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Ethylene Glycol Chemical Engineering Final Year Project
MATERIAL BALANCE The two reactions taking place in this process are given below. C2H4 + ½ O2 C2H4 + 3O2
C2H4O (main reaction) 2CO2 + 2H2O (side reaction
Molecular Weights: Component Component
Molecular weights
Ethylene
28
Oxygen
32
Ethylene oxide (EO)
44
Carbon dioxide dioxide
44
Water
18
Nitrogen
28
Total ethylene oxide to be produced =
100 TPD.
= 100000 Kgs/ day. = 4166.67 Kgs/ hr.
Basis: 1 Hour of operation REACTOR: Total weight of ethylene oxide is to be produced = 4166.67 Kgs. Assuming 2% of the EO produced is lost during the production. Total EO to be produced = 4250 Kgs/ hr. = 96.59 Kg moles/ hr. Assuming a conversion of 50% of ethylene fed and in that 25 % of the ethylene is converted into ethylene oxide. Ethylene to be supplied= 96.59/ 0.25 = 386.36 Kg moles/ hr. = 386.36 X 28 = 10818.1 Kgs/ hr Air to Ethylene ratio is 10:1 Air supplied (95 Mole % oxygen and rest is assumed to be nitrogen) = 10818.1 X10 = 108181 Kgs/ hr Molecular weight of the air supplied = (0.95 X 32 + 0.05 X 28) = 31.8 Air supplied = 108181/ 31.8 = 3401.92 Kg moles/ hr Ethylene converted to ethylene oxide = 386.36 X 0.25 = 96.59 Kg moles/ hr. = 2704.52 kgs/ hr. EO produced = 96.59 Kg moles/ hr = 4250 kgs/ hr. Ethylene converted into water and carbon dioxide = 96.59 Kg moles / hr = 2704.52 Kgs/ hr.
Carbon dioxide produced = 96.59 X 2 = 193.18 Kg moles/ hr = 8500 Kgs/ hr. Water produced = 96.59 X 2 = 193.18 Kg moles/ hr. = 3477.24 Kgs/ hr. Ethylene unreacted = 10818.1- (2704.52 X 2) = 5409.06 Kgs/hr = 193.18 Kg moles / hr
Oxygen required for both the reactions. Oxygen entering = 103148.37 Kgs/ hr = 3231.824 Kg moles/ hr. Nitrogen entering = 5032.63 Kgs/ hr = 179.73 Kg moles/ hr. Oxygen needed for the production of EO = 96.59/ 2 = 48.295 Kg moles/ hr. = 1545.44 Kgs/ hr. Oxygen needed for water and carbon dioxide = 96.59 X 3 = 289.77 Kg moles/hr = 9272.64 Kgs/ hr. Oxygen unreacted = 103148.37 - (1545.44 + 9272.64) = 92330.29 Kgs/ hr = 2885.32 Kg moles/hr. Nitrogen leaving the reactor = 5032.63 Kgs/ hr.
INPUT TO THE REACTOR: Ethylene
= 10818.1 Kgs/ hr
Oxygen
= 103148.37 Kgs/ hr
Nitrogen
= 5032.63 Kgs/ hr
Total
= 118999 Kgs/ hr
OUTPUT FORM THE REACTOR: Ethylene oxide
= 4250 Kg/ hr
Ethylene unreacted
= 5409.06 Kgs /hr
Oxygen unreacted
= 92330.29 Kgs/ hr
Nitrogen
= 5032.63 Kgs/ hr
Carbon dioxide
= 8500 Kgs/ hr
Water
= 3477.24 Kgs/ hr
Total
= 118999 Kgs/ hr
Ethylene oxide Ethylene
Unreacted ethylene
Oxygen
Unreacted oxygen
Nitrogen
REACTOR
Nitrogen Carbon dioxide Water
WATER ABSORBER: The solubility of EO in water is infinity. So the amount of water required for the absorption of EO is the equal amount of water. Water used for absorption = 4250 X1.10 = 4675 Kgs/hr (10 % of extra water is used to scrub all the EO produced.) Total EO scrubbed = 4250 Kg/ hr Solubility data: Component
Solubility (Kgs/ Kgs of water)
Nitrogen
1.3462 X 10-5
Carbon dioxide
1.379 X 10-3
Oxygen
2.87 X 10 -5
Ethylene
1.482 X 10-2
During the absorption EO in water oxygen, nitrogen, carbon dioxide and ethylene is also absorbed in smaller quantities. Nitrogen absorbed = 4675 X1.3462 X 10 -5 = 0.0629 Kgs/ hr Carbon dioxide absorbed = 4675 X 1.379 X 10 -3 = 6.4 Kgs/ hr Ethylene absorbed = 4675 X 1.482 X 10-2 = 69.2835 Kgs/ hr Oxygen absorbed = 4675 X 2.87 X 10
RECYCLE AND PURGE STREAM FORM THE ABSORBER: Ethylene
= 5340 Kgs/ hr
Oxygen
= 92330.156 Kgs/hr
Carbon dioxide
= 8493.6 Kgs/ hr
Nitrogen
= 5032.56 Kgs/hr
EO
= 21.2 Kgs/ hr
Total
= 111217.5 Kgs/ hr
OUTPUT FROM THE ABSORBER: EO
= 4228.8 Kgs/ hr
Oxygen
= 0.134 Kgs/ hr
Nitrogen
= 0.0629 Kgs/ hr
Carbon dioxide
= 6.4 Kgs/ hr
Water
= 8152.24 Kgs/ hr
Ethylene
= 69.2835 Kgs/ hr
Total
= 12456.92 Kgs/ hr
Total
= 123674Kgs/ hr
Recycle and purge gases
Water
W A T E R A B S O R B E R Input
Output
DESORBER: The amount of used for absorbing the ethylene oxide in the absorber is desorbed in the desorber and recycled. 0.5% of the produced ethylene oxide is also lost with the water. RECYCLE STRAEM FROM THE DESORBER: Water recycled
= 4675 Kgs/ hr
EO lost
= 21.14 Kgs/ hr
Total
= 4696.144 Kgs/ hr
INPUT TO THE DESORBER: EO
= 4228.8 Kgs/ hr
Oxygen
= 0.134 Kgs/ hr
Nitrogen
= 0.0629 Kgs/ hr
Carbon dioxide
= 6.4 Kgs/ hr
Water
= 8152.24 Kgs/ hr
Ethylene
= 69.2835 Kgs/ hr
Total
= 12456.92 Kgs/ hr
OUTPUT FROM THE DESORBSER: EO
= 4206.8 Kgs/ hr
Oxygen
= 0.134 Kgs/ hr
Nitrogen
= 0.0629 Kgs/ hr
Carbon dioxide
= 6.4 Kgs/ hr
Water
= 3477.24 Kgs/ hr
Ethylene
= 69.2835 Kgs/ hr
Total
= 7760 Kgs/ hr
Output from the desorber
Input to the desorber
D E S O R B E R
Recycled water STEAM STRIPPER: Steam at a pressure of 1.5 bars is used for stripping the vent gases. INPUT TO THE STRIPPER: EO
= 4206.8 Kgs/ hr
Oxygen
= 0.134 Kgs/ hr
Nitrogen
= 0.0629 Kgs/ hr
Carbon dioxide
= 6.4 Kgs/ hr
Water
= 3477.24 Kgs/ hr
Ethylene
= 69.2835 Kgs/ hr
Total
= 7760.776 Kgs/ hr
OUTPUT FROM THE STRIPPER: EO
= 4206.86 Kgs/ hr
Water
= 3477.24 Kgs/ hr
Ethylene
= 69.2835 Kgs/ hr
Total
= 7753.3835 Kgs/hr
VENT GASES: Carbon dioxide
= 6.4 Kgs/ hr
Nitrogen
= 0.0629 Kgs/ hr
Oxygen
= 0.134 Kgs/ hr
Total
= 6.5969 Kgs/ hr Vent gases
Input
STEAM STRIPPER Steam
Output from the stripper
REFINING STILL: INPUT TO THE REFINING STILL: EO
= 4206.86 Kgs/ hr
Water
= 3477.24 Kgs/ hr
Ethylene
= 69.2835 Kgs/ hr
Total
= 7753.3835 Kgs/hr
Input in Kg moles/ hr (F)= 290.71 Kg moles/ hr xF = mole fraction for ethylene oxide in feed = 95.133/ 290.17= 0.33 Distillate = 4166.67 Kgs/ hr = 4166.61/ (0.999 X 44 + 0.001X 18) (D) = 94.65 Kg moles/ hr xD = mole fraction of ethylene oxide in the distillate.(commercial grade ethylene oxide) = 0.99 F= D+W 290.71= 94.65 + W W= 196.06 Kg moles/ hr = 3586.77 Kgs/hr F* xF = D* xD + W* xW
xW = mole fraction of ethylene oxide in the bottom stream 290.71 X 0.33 = 94.65 X 0.99 + 196.06 X x W xW = 0.012 Reflux ration calculation is given in the detailed design procedure of the process. Reflux ratio = 0.25 L0 / D = 0.25 L0 = 0.25 X 94.65 = 23.66 Kg moles/ hr = 1040.42 Kgs/ hr OUTPUT FROM THE REFINING STILL: Ethylene oxide
